A conventional NMR imaging apparatus is, as shown in FIG. 4, composed of a static magnetic field coil 2 which is urged by a power source and driver 1 for generating a uniform and stable static magnetic field; a probe head (RF coil) 4 which is urged by the power source and driver 1 for generating an RF pulse, and which detects an NMR signal of an object to be examined and supplies it to a preamplifier and detector 3; a gradient magnetic field coil 5 which is urged by the power source and driver 1 for generating linear gradient magnetic fields in the three directions of x, y and z which overlap the static magnetic field; an A/D converter 14 for converting an output signal of the preamplifier and detector 3 into digital data; and a computer system 6 for controlling the power source and driver 1 and the preamplifier and detector 3 and for processing the digital data supplied from the A/D converter 14. The computer system 6 is composed of a central processing unit (CPU) 7, a sequence controller 8, an image display (CRT) 9, a memory (DISK) 10, an array processor (AP) 11 provided with a high-speed memory, an input/output device (I/O) 12, a system bus 13 for connecting these members 7 through 12 to each other, and an A/D converter 14 connected to the I/O 12.
FIG. 5 schematically shows the relationship between a slice and a view with respect to an object to be examined in the case of acquiring data by a multislice multiecho method (hereinunder an image at the same slice which has a different echo time will be defined as a slice in a broad sense), for example, by the Fourier method by means of such a conventional NMR imaging apparatus. In FIG. 5, the reference numeral 15 represents an object to be examined, and the symbol m represents the number of slices and n the number of views. Ordinarily, k items of sample data are acquired in one measurement, and such measurement is repeated j times per view in order to obtain the average measured data.
The operation of the NMR imaging apparatus is as follows. In the actual apparatus, the number m of slices is typically 32 and the number j of measurements for averaging is typically 8, but hereinunder it is assumed that the number m of slices is 2, the number n of views 256, the number of items of data 256, and the number j of measurements 2, for the purpose of simplifying the explanation.
When the sequence controller 6 drives the power source and driver 1 at a constant timing on the basis of a command from the CPU 7, the probe head 4 is energized and the current of the gradient magnetic filed coil 5 is turned on and off, as is required for measurement of an NMR signal. It goes without saying that a uniform and static magnetic field has been generated in advance by the static magnetic field coil 2. After the base band of an NMR signal received by the probe head 4 is converted into an audio frequency by the preamplifier and detector 3, the NMR signal is supplied to the A/D converter 14.
The pulse sequence at this time is carried out in such a manner as is indicated by (a), (b), (c) and (d) in FIG. 6. (a), (b), (c) and (d) in FIG. 6 represent the timing for energizing the probe head, and the timings for applying gradient magnetic field in the directions of x, y and z, respectively. In correspondence with these operations, an NMR signal such as a free induction decay signal (FID signal) indicated by (e) in FIG. 6 is detected.
NMR signals E.sub.m /(#n, j) are acquired in the order of detection as shown in the column A of FIG. 7, and are stored in the DISK 10 in that order. The measured value of an NMR signal E.sub.m (#n, j) is composed of k items of sample data. The data stored in the DISK 10 are arranged in such a manner that the data measured at a first time at one view are arranged in the order of slices, and the data measured at a second time in the same view are next arranged in the order of slices, and such arrangement is repeated for every view. Therefore, measured data are very complicated with respect to a slice, and the data on the same slice are not collected at the same place. The CPU 7 calculates {E.sub.1 (#1, 1)+E.sub.1 (#1, 2)}/2 to obtain the average value of the data E.sub.1 (#1, 1) on the slice 1 measured at first time at a view 1 and the data E.sub.2 (#1, 2) on the slice 1 measured at a second time at the view 1. The average value E.sub.1 (#1) obtained is re-stored in the DISK 10 as a raw data on the slice 1 at the view 1. The CPU 7 executes a similar averaging calculation about all the data on each slice at all the views, and all the average values obtained are subsequently re-stored in the DISK 10. Thus, the averaged raw data E.sub.1 (#1), E.sub.2 (#1), . . . E.sub.1 (#256), E.sub.2 (#256) are re-stored in the DISK 10 in the order shown in the column B of FIG. 7. In this state, the arrangement of the data is still complicated with respect to a slice.
When the image is reconstructed, the CPU 7 picks up the data E.sub.1 (#1), E.sub.1 (#2), . . . E.sub.1 (#256) on the slice 1, for example, from the data stored in this state, as shown in the column C of FIG. 6, and the AP 11 reconstructs the image of the slice 1 on the basis of the collected data. The reconstructed image is displayed on the CRT 9. When the image of the slice 2 is reconstructed, the CPU 7 and the AP 11 execute a similar processing on the data E.sub.2 (#1), E.sub.2 (#2), . . . E.sub.2 (#256).
Such a conventional NMR imaging apparatus is disadvantageous in that since measured data are stored in a large-capacity memory in the order of acquisition in a complicated state with respect to a slice, and an image is reconstructed by picking up raw data on the corresponding slice from data stored in such a state, a heavy load is applied to the CPU 7 or the AP 11, so that the speed of reconstruction of a image is lowered.